Figure 6. All detected California events (29), false events (squares, 2), and missed events (circles, 3) with M≥3.5 that occurred between 2 October 2012 and 15 February 2013. ANSS epicenters (filled stars) and the corresponding E2 epicenters (open stars) are connected with a line. Errors in source parameters are minimal within regions of high station density and increase in regions offshore and outside of California, such as near Cape Mendocino and south of the California–Mexico border. The two alert regions described in the text are shown as the San Francisco Bay Area (SFBA, northern) and Los Angeles (LA, southern) boxes and are areas with high densities of both population and seismic stations.

Abstract
The California Integrated Seismic Network (CISN) is developing an earthquake early warning (EEW) demonstration system for the state of California. Within this CISN ShakeAlert project, three algorithms are being tested, one of which is the network-based Earthquake Alarm Systems (ElarmS) EEW system. Over the last three years, the ElarmS algorithms have undergone a large-scale reassessment and have been recoded to solve technological and methodological challenges. The improved algorithms in the new production-grade version of the ElarmS version 2 (referred to as ElarmS-2 or E2) code maximize the current seismic network’s configuration, hardware, and software per- formance capabilities, improving both the speed of the early warning processing and the accuracy of the warnings. E2 is designed as a modular code and consists of a new event monitor module with an improved associator that allows for more rapid association with fewer triggers, while also adding several new alert filter checks that help minimize false alarms. Here, we outline the methodology and summarize the performance of this new online real-time system. The online performance from 2 October 2012 to 15 February 2013 shows, on average, ElarmS currently issues an alert 8:68 +/- 3:73 s after the first P-wave detection for all events across California. This time is reduced by 2 s in regions with dense station instrumentation. Standard deviations of magnitude, origin time are 0.4 magnitude units, 1.2 s, and the median location errors is 3.8 km. E2 successfully detected 26 of 29 earthquakes (M-ANSS > 3.5) across California, while issuing two false alarms. E2 is now delivering alerts to ShakeAlert, which in turn distributes warnings to test users.